A solid oxide fuel cell (SOFC) referred to as a third-generation fuel cell is a fuel cell using a solid oxide allowing permeation of oxygen or hydrogen ions as an electrolyte, and was first operated by Bauer and Preis in 1937. An SOFC operates at the highest temperature (700° C. to 1,000° C.) in existing fuel cells. All constituents are made of solid, and accordingly, the structure is simpler compared to other fuel cell structures, and there are no problems of electrolyte loss and replenishment, and corrosion. In addition, precious metal catalysts are not required since an SOFC operates at a high temperature, and fuel supply through direct internal reforming is readily obtained. An SOFC also has an advantage in that heat combined generation using waste heat is possible since the SOFC emits high temperature gas. Due to such advantages, researches on SOFCs have been actively carried out with a purpose of commercialization in the early 21st century.
General SOFCs are formed with an oxygen ion conductive electrolyte, and an air electrode (cathode) and a fuel electrode (anode) located on both sides of the electrolyte. A basic operation principle of an SOFC is that oxygen ions produced from an oxygen reduction reaction in an air electrode migrate to a fuel electrode through an electrolyte, and then react again with hydrogen supplied to the fuel electrode to produce water, and herein, electrons are produced in the fuel electrode, and electrons are consumed in the air electrode, and therefore, a current is generated by connecting the two electrodes. FIG. 1 is a diagram showing one example of an operation principle of a solid oxide fuel cell. In other words, oxygen introduced through an air electrode and hydrogen introduced from a fuel electrode reacts to generate a current.
An air electrode and a fuel electrode of an SOFC need to have high porosity, and an electrolyte provided in between needs to have a dense structure. Accordingly, a baking process is individually carried out in order to prepare these, and in the case of an electrolyte that needs to have a dense structure, baking needs to be carried out at a particularly high temperature. As a result, there have been problems in that distortion between each constitution occurs due to differences in the sintering temperatures, and process costs increase since each constitution is separately baked.